1. Field of the Invention
The invention relates to buoyant riser systems, and more particularly, to buoyant riser systems utilizing inflatable bladders to provide the requisite buoyancy.
2. Description of the Prior Art
In offshore drilling systems, a riser extends from the blowout preventers at the ocean floor to the drilling vessel floating on the ocean surface. When a storm such as a hurricane approaches the drilling site, it is necessary for the drilling vessel to disconnect from the well. Typically, the riser is disconnected at the ocean floor, and the entire riser must be retrieved and laid down in joints on the floating vessel. A substantial period of time is required to accomplish such disconnect operations, and there is a very significant accompanying cost for drilling vessel down time. It is not uncommon in locations such as the Gulf of Mexico for a drilling ship to have to disconnect several times because of approaching storms during a typical hurricane season.
It has also been proposed to utilize buoyant risers wherein a substantial portion of the riser above the ocean floor is buoyant so that it can be disconnected from the drilling vessel. U.S. Pat. No. 4,234,047 to Mott discloses such a disconnectable buoyant riser system. These systems have typically been proposed utilizing rigid steel cans for buoyancy. Mott suggests with regard to FIGS. 6 and 7 thereof the use of collapsible flexible walled buoyancy tanks.
Jacobs and Homer, "Development of the 13,200 ft. Riser for the Ocean Margin Drilling Program" have proposed another design for a freestanding buoyant riser system using rigid can type flotation.
Inflatable bladders like those proposed for use in the present invention as buoyancy members are available in the art for other purposes. Yokohama Catalog No. CN-0303S-02E entitled "Yokohama Floating Fenders Pneumatic 50 and 80" discloses floating inflatable fenders.
Thus, although the art has included suggestions for the use of inflatable buoyancy tanks on risers as shown in the Mott U.S. Pat. No. 4,234,047, no workable system for the use of inflatable buoyancy elements on risers has yet been proposed.